The present state of technological development allows magnetic fields, e.g. of current conductors, to be measured by magnetic-field sensors, e.g. Hall-effect sensors. Flux concentrators are used to measure very small magnetic fields, as well, with the aid of such magnetic-field sensors. Such flux concentrators are essentially made up of high-permeability materials, which are positioned with respect to the magnetic field to be measured, in such a manner, that an increase in the measuring sensitivity results from the combination of a magnetic-field sensor and a flux concentrator. A disadvantage of flux concentrators is that they may show saturation effects and signs of hysteresis. In addition, the space requirements and the costs of flux concentrators are disadvantageous.